One of the best procedures for preventing the spread of the coronavirus is a lockdown, if it is implemented correctly. In order to assess how well lockdowns prevent the virus’s propagation, this paper presents a fractional-order mathematical model constructed by the proportional-Caputo operator. This model consists of five nonlinear fractional-order differential equations. The solution’s existence and uniqueness are investigated using the Schauder and Banach fixed-point theorems. Also, this study produces a stability analysis utilizing Ulam–Hyers and modified Ulam–Hyers criteria. Furthermore, the Adams–Bashforth–Moulton approach is used to implement numerical simulations that show how the model behaves with different parameter combinations and to validate the theoretical results.